diff --git a/openedx/core/lib/cache_utils.py b/openedx/core/lib/cache_utils.py
index e9157586b2..2c80516b8b 100644
--- a/openedx/core/lib/cache_utils.py
+++ b/openedx/core/lib/cache_utils.py
@@ -151,7 +151,7 @@ class process_cached(object):  # pylint: disable=invalid-name
 
 def zpickle(data):
     """Given any data structure, returns a zlib compressed pickled serialization."""
-    return zlib.compress(pickle.dumps(data, pickle.HIGHEST_PROTOCOL))
+    return zlib.compress(pickle.dumps(data, 2))  # Keep this constant as we upgrade from python 2 to 3.
 
 
 def zunpickle(zdata):